1. News from TBTS International Workshop on Future Linear Colliders,
Ganada, Spain, 2011,
Alexey Dubrovskiy

2. Outlines Layout Deceleration Acceleration Improvements
PETS & RF components processing
TD24 processing
Breakdown kick measurements
“Flash box”
Proposal
Alexey Dubrovskiy
LCWS2011 2

3. CTF & TBTS layout
Alexey Dubrovskiy
LCWS2011 3

4. Deceleration & RF Recirculation
Alexey Dubrovskiy
LCWS2011
RF extraction and recirculation model agrees with RF measurements
* Eric Adli (University of Oslo) 4 4

5. Deceleration & RF Recirculation
Alexey Dubrovskiy
LCWS2011
Extracted RF power measurements agree with beam energy measurements apart of a calibration factor.
* Eric Adli (University of Oslo) 5 5

6. PETS RF power extraction
Measured RF power extraction MW
CLIC requirement
Alexey Dubrovskiy
LCWS2011 ns
The extracted RF from the PETS exceeds the CLIC requirement by about a factor 2 in power. 6

7. Accelerating structure in 2010
Alexey Dubrovskiy
LCWS2011
* Oleksiy Kononenko (CERN)
10 Mhz structure detuning was confirmed during the winter shutdown in Jan 2011.
The deformation could appear when clamping the cooling circuit onto the structure.
The structure was retuned and it was put back.
In spring 2011 RF measurements showed the right tuning frequency.
* Jiaru Shi (CERN) 7

8. Acceleration 8 Alexey Dubrovskiy LCWS2011 27.09.11 RF in RF out
Accelerating structure
Beam profile monitor
Alexey Dubrovskiy
LCWS2011
With RF
No RF
The acceleration of 145 MeV/m has been achieved.
(CLIC acc.g. is 100 MV/m) 8 8

9. RF measurements Estimated Acceleration from Diodes Drive beam
PETS 12GHz
PETS output
Loop output
Alexey Dubrovskiy
LCWS2011
ACS output
Estimated Acceleration from IQs
ACS input
Probe beam
TD24_vg1.8_disk
- RF Diode & IQ measurements
All Diode and PETS and Loop output IQ signals are consistent with acceleration. 9

10. CTF3 night operation
Alexey Dubrovskiy
LCWS2011
Successful run over nights with the stable beam conditions allowed to measure breakdown rates of RF components. 11 10

11. BD detection Drive beam PETS 12GHz Probe beam TD24_vg1.8_disk
PETS output
Loop output
ACS output
ACS input
Probe beam
Alexey Dubrovskiy
LCWS2011
TD24_vg1.8_disk
- RF Diode & IQ measurements of forward and reflected RF
Faraday cup
Photomultiplier
Breakdowns in the recirculation loop are detected only from the reflected power (Pref / Pfwd > ~15%).
Breakdowns in attenuator and the waveguide are detected from the missing energy (Utran / (Ufwd * transmission factor) > 15%)
Breakdowns in the ACS are detected from the reflected power, the missing energy, the Faraday cup and the photomultiplier. 10 11

12. Illustration of BDs PETS extracted PETS reflected Attenuated forward
Attenuated reflected
BD without reflection
Alexey Dubrovskiy
LCWS2011
ACS reflected
ACS forward
BD in the waveguide
ACS transmitted
Drive beam current
No BD 12

13. PETS: Processing Vacuum level PETS peak power
Pulse length at 75% of pp
Pulse length at 90% of pp
Alexey Dubrovskiy
LCWS2011
Number of BD
BDR 13

14. Attenuator: Processing
PETS peak power
Attenuated peak power
Pulse length at 75% of pp
Pulse length at 90% of pp
Alexey Dubrovskiy
LCWS2011
Number of BD
BDR 14

15. Waveguide: Processing
Peak power
Pulse length at 75% of pp
Pulse length at 90% of pp
Alexey Dubrovskiy
LCWS2011
Number of BD
BDR 15

16. TD24: parameters 42.2 TD24_vg1.8_disk 120o/ cell comments f [GHz]
11.995
S12
0.6542
tf [ns]
64.55
QCu
5732
Gradient averaged over all cells
V26 = 1 W
3340
2 matching +24 regular cells
Lacc = mm,
G26 = 1 W
14661
Pin
46.5
Gradient averaged over regular cells only
V24 = 1 W
3078
24 regular cells only
Lacc = mm,
G24 = 1 W
15390
Pin
42.2
Alexey Dubrovskiy
LCWS2011
* A. Grudiev, 25/03/10 16

17. TD24: Summary of processing
Period
Pulses
Number of BD
2010
1.5 MPulses
40 kBD
2011 beginning
250 kPulses
2.5 kBD
2011 summer
608 kPulses
10 kBD
Total
2.4 MPulses
53 kBD
This period is considered in the following slides
Alexey Dubrovskiy
LCWS2011
* At the beginning of 2011 the ACS was taken out and retuned 17

18. TD24: Processing Forward peak power Vacuum level
Pulse length at 75% of pp
Pulse length at 90% of pp
Alexey Dubrovskiy
LCWS2011
Number of BD
BDR 18

19. Explicit BDR measurements
bdpppm
Alexey Dubrovskiy
LCWS2011
MV / m
BDR is scaled to a pulse length of 160ns:
vertical lines: slim - τ6 and bold - τ3.
Horizontal bold lines show the standard deviation of the accelerating gradient variation during the period. 19

20. TD24: 3 Periods Forward peak power Vacuum level 1 2 3 1 2 3 Periods
Pulse length at 75% of pp
Pulse length at 90% of pp
Alexey Dubrovskiy
LCWS2011
Number of BD
BDR 20

21. BDR scaling low for traveling wave structures
BDR scaling low for any pulse:
BDR ~ (∫ E(t)s1/s2 dt)s2 (E - field and s1,s2 – const.)
BDR scaling low for a rectangular pulse (E(t)=Ec) of a pulse length of τ:
BDR ~ Ecs1τs2 (Ec and τ – const.)
In case if the s2/s1=4, the breakdown rate strongly depends on the pulsed surface heating.
This allows to normalize any pulse to a certain gradient or a pulse length:
1) Normalization low to the rectangular pulse of a pulse length of 160ns:
Ec = (∫E(t)s1/s2 dt / 160)s2/s1
Alexey Dubrovskiy
LCWS2011
2) Normalization low to the rectangular pulse of an accelerating gradient of 100 MV/m:
τ = ∫E(t)s1/s2 dt / 100 s1/s2
s1=30, s2=5
s1=12, s2=3
Yellow lines – forward power; red lines – Ec low scaling; blue lines – τ low scaling. 21

22. TD24: Accelerating gradient vs BDR
From data fitting:
Period 1: Ec ~ τ1/3.7
Period 2: Ec ~ τ1/3.4
Period 3: Ec ~ τ1/3.9
Alexey Dubrovskiy
LCWS2011
BDR scaling low for rectangular pulses:
BDR ~ Ecs1τs2 (Ec and τ – const.)
Normalization low to the rectangular pulse of a pulse length of 160ns:
Ec = (∫E(t)s1/s2 dt / 160)s2/s1 22

23. TD24: Pulse length vs BDR From data fitting: Period 1: Ec ~ τ1/3.9
Alexey Dubrovskiy
LCWS2011
BDR scaling low for rectangular pulses:
BDR ~ Ecs1τs2 (Ec and τ – const.)
Normalization low to the rectangular pulse of an accelerating gradient of 100 MV/m:
τ = ∫E(t)s1/s2 dt / 100s1/s2 23

24. TD24: Stress vs BDR bdpppm MV / m
Alexey Dubrovskiy
LCWS2011
MV / m
BDR scaling low for rectangular pulses and constant temperature:
BDR ~ exp(a Ec2) (Ec– const.)
* Flyura Djurabekova ( )
Normalization low to the rectangular pulse of a pulse length of 160ns:
Ec = (∫E(t)4 dt / 160)1/4 24

25. TD24: Pulsed surface heating
Alexey Dubrovskiy
LCWS2011 25

26. TD24: Breakdown distribution
Alexey Dubrovskiy
LCWS2011 26

27. TD24: Vacuum level
Alexey Dubrovskiy
LCWS2011 27

28. Breakdown kick measurement
(0.46, 1.63)
( )
Beam kick on OTR screen
1.7 mm
kick angle ≈ 0.4 mrad
Alexey Dubrovskiy
LCWS2011
* Andrea Palaia (Uppsala University)
Probe beam
~194 MeV
ACS
OTR
0.4 mrad 28

29. FLASH box is installed ACS Flash box Probe beam line
“Flash box” is installed in TBTS just before the accelerating structure. It will allow to detect particles emitted during BD and to estimate its energies.
All plates in the “Flash box” detect something during a BD in ACS. This study is still going on.
There are three consecutive pulses illustrated on each picture. Only the pulse shown with blue lines has a BD in the ACS.
ACS ref power
ACS fwd power
ACS tran power
Drive beam current
Alexey Dubrovskiy
LCWS2011
Some signals from FLASH plates
* Tomoko Muranaka (Uppsala University) 29

30. Proposal: Mode of Operation
TD24 mode of operation:
The increase in power provokes a BD.
The reduction in power reduces the probability of a BD.
Pr(BD | Pi-1<Pi) / Pr(BD) = 1.14
Pr(BD | Pi-1>Pi) / Pr(BD) = 0.86
CLIC mode of operation could be in two phases:
Normal two beam operation. (many pulses )
The probe beam is switched off and the PETS peak power is increased (using the ON/OFF mechanism?). This will allow to inhibit several BDs at different places at the same time. Hence the ACS and RF system BDR limitation can be relaxed. (a few pulses <0.1%)
Alexey Dubrovskiy
LCWS2011
Systematic experiments are needed in order to estimate the effectiveness of such mode of operation.
The result of such experiments can help to answer on the important question on “memory” of the structure. 30

31. Summary
The PETS deceleration and power extraction models have been validated with RF and beam measurements.
It has been measured that PETS can extracted two times higher power > 260MW than CLIC needs.
The TD24 has been retuned. And an acceleration gradient of the probe beam has been measured with beam at 145MeV/m, which is above the CLIC requirement 100MeV/m. This result agrees with the RF measurements.
The major limitation to go beyond this values is the RF power splitter, which is already taken out. And the recirculation scheme will be replaced by the PETS ON/OFF mechanism.
The TD24 breakdown rate has been measured down to The scaling low is estimated as ~E12τ3 in stead of the expected scaling low E30τ3. This is an indication that the pulsed surface heating plays significant role in BDR.
There is a “hot” cell or region in TD24, where BDs happen more often.
The measured vacuum activity indicates that it can be a change for CLIC. More study is needed.
Breakdown kick has a strong impact on the probe beam.
The “flash box” is installed and I hope it will show new results soon.
There were proposed a generalization BDR scaling low and a new mode of operation of ACSs, which might help to relax the CLIC BDR limitation from 10-7 up to between 10-5 and 10-6.
Alexey Dubrovskiy
LCWS2011 31

32. Appendix: TD24 Gradient in 24 regular cells
Average unloaded of 100 MV/m
Average loaded of 100 MV/m
Number of regular cells: Nc 24
Bunch population: N
3.72x109
Number of bunches: Nb
312
Bunch separation: Ncycl
6 rf cycles
* A. Grudiev, 25/03/10